As the recent development of high-tech electronics industry allows miniaturization and weight lightening of electronic devices, portable electronic devices are increasingly used. Batteries having a high energy density are much more required as the power supply of such portable electronic devices and thus researches for a lithium secondary battery are actively pursued. The lithium secondary battery includes a lithium ion battery, a lithium sulfur battery, a lithium-air battery, and the like.
In addition, the research for improving energy density, safety, and the like in the lithium secondary battery is continuously required. For example, the research on the innovative conversion system in the transition insertion chemistry has been done, one of which is about lithium sulfur system.
The lithium sulfur system is a system based on the reaction of 16Li+S8→8Li2S, which can obtain much high energy (2,500 Whkg−1) than that of the existing lithium ion battery (500 Whkg−1). Since the lithium sulfur battery uses high-capacity substances of sulfur and a lithium metal instead of those substances (positive electrode lithium cobalt oxide/negative electrode carbon) mainly used for the positive electrode and the negative electrode of the existing lithium ion battery and lithium ion polymer battery, it can give 3 to 5 times larger capacity than the existing lithium ion battery or lithium ion polymer battery and it can also give such advantages of a low price and being environmentally friendly. Thus, it has been noted as a next-generation secondary battery.
The lithium sulfur battery generally uses a sulfur-based material having an S—S bond (Sulfur-Sulfur linkage) as a positive electrode active material and a carbon-based material which is capable of insertion/deinsertion of an alkali metal such as lithium or a metal ion such as a lithium ion, and the like as a negative electrode active material. The lithium sulfur battery uses a redox reaction for the storage and generation of electric energy, wherein the S—S bond is broken while decreasing the oxidation number of S during the reduction reaction (when discharged) and the S—S bond is formed again while increasing the oxidation number of S during the oxidation reaction (when charged).
However, the lithium sulfur battery has such problems that it is difficult to maintain the structure of sulfur/carbon charge/discharge composite based on aqueous/non-aqueous polymers, the areal electrode loading is low (<2 mAh/cm2) due to the low adhesiveness between the ground electrode and the composite, and it has insufficient ability of suppressing the elution of lithium-polysulfide.